Hey guys, I just wanted to know your opinion on the largest streetable cams for a DD (but autoxed) ae86.
I was leaning towards 288s, are those doable? What lift would you recommend? I was hoping to get up to a nice 8000-8500rpm red line (after all of the appropriate valve train modifications).
Thanks guys!

What kind of intake set up will you be running?

There are different definitions of "streetable". I don't DD my car, so as long as it idles at red lights, I would consider it streetable; even if it idled around 3 grand and pulled to 12. You have to decide how uncomfortable you are willing to be.

I'll be running silver top ITBs

BosoHachi wrote:I'll be running silver top ITBs

If youre running an ITB set up where the ITBS dont share an intake chamber (Open itbs, individually filtered ITBs, etc- As this is a self proclaimed DD however I STRONGLY recommend individually filtered out of these options), you can use damn near any size cam you want.

High duration/lift cams are idled higher because they are (well, CAN be) "lopey" at low rpms. This "lopey" tendency can cause stalling, and diminishes as the rpms are increased.

What causes this lopey behavior is the result of how cams of this type behave at low rpms. Cams have whats called "overlap", that is when the intake and exhaust valves are open at the same time. It goes without saying that at lower rpms, the physical window/time frame in which these valve are opened together is physically longer. At low engine speeds this overlap is long enough that a cylinders that is ingesting air, can literally suck exhaust gases straight out of the exhaust manifold from neighboring cylinders which are currently overlapping and have both valves open. This causes improper air/fuel ratios in the cylinder- and they dont fire properly. As the engine speeds pick up this no longer poses an issue.

ITBs which dont share a common chamber, dont suck the exhaust gases back through from neighboring cylinders, and run just fine. This is why an ITB powered car can idle damn near any useable cam profile like it was stock.

No lopey cam. No ridiculous high idle. You can DD relatively easily whatever the hell you want.

Oh, and if ANYONE ever tells you "Ya but high profile/lift/duration/whatever cams make no power down low!". Smack them. Smack the **** out of them. And then smack them again. Maybe teabag them when theyre dazed on the floor for good measure. This concept is bullshit, and unfounded in reality. You need look no further than the extreme examples of our cars- Google for dynographs from some of the most extreme 4age builds. Hasselgrens, formula atlantics, N2 ae86s, etc. They all make about 70-80% of their peak torque from as low as a couple thousand rpms. Thats typically more torque than our factory 4ages make at peak. They have PLENTY of power to get moving. The idea stems from how the cars accelerate as they approach their actual power bands. It may "feel" slow, compared to how it pulls in its power band, but its still physically moving just fine.

SidewaysGts wrote:

BosoHachi wrote:I'll be running silver top ITBs

If youre running an ITB set up where the ITBS dont share an intake chamber (Open itbs, individually filtered ITBs, etc- As this is a self proclaimed DD however I STRONGLY recommend individually filtered out of these options), you can use damn near any size cam you want.

High duration/lift cams are idled higher because they are (well, CAN be) "lopey" at low rpms. This "lopey" tendency can cause stalling, and diminishes as the rpms are increased.

What causes this lopey behavior is the result of how cams of this type behave at low rpms. Cams have whats called "overlap", that is when the intake and exhaust valves are open at the same time. It goes without saying that at lower rpms, the physical window/time frame in which these valve are opened together is physically longer. At low engine speeds this overlap is long enough that a cylinders that is ingesting air, can literally suck exhaust gases straight out of the exhaust manifold from neighboring cylinders which are currently overlapping and have both valves open. This causes improper air/fuel ratios in the cylinder- and they dont fire properly. As the engine speeds pick up this no longer poses an issue.

You were doing pretty good until you got to here. First off I am going to assume you meant

can literally suck exhaust gases straight out of the intake manifold from neighboring cylinders

because what you said makes absolutely no sense.
Even if you did mean intake manifold you still missed the mark. Overlap at low rpms causes exhaust gasses to be pushed through the intake valve into the runners. Whether single TB or multi TB is irrelevant and the concern has nothing to do with other cylinders sucking in exhaust gasses. The issue is that once those exhaust gasses have been pushed up the runner are sucked back into the chamber with the fresh air and fuel. If there is too much exhaust gas then you get poor combustion and poor idle. This will happen on any intake setup. If you don't believe me then go ground out the VVT on a 20V idling some time.

Oh, and if ANYONE ever tells you "Ya but high profile/lift/duration/whatever cams make no power down low!". Smack them. Smack the **** out of them. And then smack them again. Maybe teabag them when theyre dazed on the floor for good measure. This concept is bullshit, and unfounded in reality. You need look no further than the extreme examples of our cars- Google for dynographs from some of the most extreme 4age builds. Hasselgrens, formula atlantics, N2 ae86s, etc. They all make about 70-80% of their peak torque from as low as a couple thousand rpms. Thats typically more torque than our factory 4ages make at peak. They have PLENTY of power to get moving. The idea stems from how the cars accelerate as they approach their actual power bands. It may "feel" slow, compared to how it pulls in its power band, but its still physically moving just fine.

Again you almost got it but fell short. Hopefully not leading to the OP getting his ass kicked for smacking people around for getting in peoples faces with half educated "facts".

To really make your point correct you have to address the rest of the system.
If you put bigger cams in your motor and don't change anything else then you will make less power down low. If you put FA sized cams in an otherwise stock car you would make wayyyy less power down low.
To combat this you have to raise the compression and tune the rest of the motor to take advantage of the system as a whole.

Here is a Tomei poncam dyno. There is a stock dyno line, a poncam on stock compression and a poncam on raised compression.
You will see the poncam on stock compression looses power till about 4000 RPM. Granted the loss at the greatest point is only about 5 hp so not huge but this is also one of the more mild cams out there. You throw in a 288 on stock compression and you will make a lot less power.

Of course with that said, if you dynoed that same motor with the stock cams and high comp pistons it would have made even more power under 4k rpm as long as you could keep it from detonating.

So you are sorta half right but when it comes to stuff like this half right can do more harm than good.
The poncam on raised compression m

Boso--

You may also want to mention which ECU you have. Standalone or piggy back for tuning sake.

I was also wondering how "streetable" 304 Toda Cams would be.
Wondering how much power would one have down low and where the power band would be in the upper revs.
And love that idle...it is what I seek:

http://www.youtube.com/watch?v=AJoiLKwpocE

thanks to everyone for all this great info, i learned a lot reading this thread

Cams have a lot more to them than just total quoted duration, for example my car idles just almost like factory yet I have cams with 292 degrees total duration. It's all in the ramp rates and cam angles. Another thing you that makes just as much of a difference to being "streetable" is how good of a tune you have, and how capable of an ECU you're using.

I'd do 272 and if I was going crazy 280 . 288 idle is rough

Shouldn't be an issue with a standalone

yoshimitsuspeed wrote:You were doing pretty good until you got to here. First off I am going to assume you meant

can literally suck exhaust gases straight out of the intake manifold from neighboring cylinders

because what you said makes absolutely no sense.

A blast from the past! Apologies on the late reply. But No- I did indeed mean exhaust manifold. Thats where exhaustgases come from.

Even if you did mean intake manifold you still missed the mark.

Oh my. please elaborate.

Overlap at low rpms causes exhaust gasses to be pushed through the intake valve into the runners. If there is too much exhaust gas then you get poor combustion and poor idle

Ah thank you- But hold up- Isnt that basically exactly what I stated? Sounds to me like youre stating overlap at low rpms can cause exhaust gases (which come from where again, btw?) to be pushed through the intake valves and then into the runners (i jest, this is exactly what you stated- apologies for the redundancy). Now, what exactly did I state? "At low engine speeds this overlap is long enough that a cylinders that is ingesting air, can literally suck exhaust gases straight out of the exhaust manifold from neighboring cylinders which are currently overlapping and have both valves open. This causes improper air/fuel ratios in the cylinder". So... wheres the discrepancy? Again, you've just stated exactly what I had.

Whether single TB or multi TB is irrelevant

Aye, totally agree 100%

and the concern has nothing to do with other cylinders sucking in exhaust gasses. The issue is that once those exhaust gasses have been pushed up the runner are sucked back into the chamber with the fresh air and fuel. If there is too much exhaust gas then you get poor combustion and poor idle.

Sooo.. The "concern has nothing to do with other cylinder sucking in exhaust gasses" it has to do with "Exhaust gasses (that) have been pushed.. into the other chamber (ie: cylinders). Wait. What?...

This will happen on any intake setup. If you don't believe me then go...

Any intake set up where the next cylinder on the intake stroke can suck up exhaust gases during long durations of overlap*. But hey- Totally believe you. I was fortunate enough to spend many years in a Tuning shop before I moved to australia, much of my time was spent assisting with dyno work- And completely found this to be true 100% of the time.

Again you almost got it but fell short. Hopefully not leading to the OP getting his ass kicked for smacking people around for getting in peoples faces with half educated "facts".

To really make your point correct you have to address the rest of the system.

If you put bigger cams in your motor and don't change anything else then you will make less power down low....

A) Ill keep this in mind the next time I see someone running nothing but a high lift/duration camshaft with zero other mods (correction- The first time I see this- As I never have to date) and B) I never said they wouldnt make less power. I said if someone says they make "no" power. this is figurative of course, But i was under the impression the context was coherent enough to properly display my intended meaning here. On my adventures I've met many, many people who believe that engines with large duration/lift cams make not simply "less" power in the low range, but make ridiculously less power down low, so little that theyre under the impression the car would be an utter dog to drive at low rpms, and has to be revved to high hell and back. This notion is completely false in every case I've ever encountered (also verified by your dyno links, thanks for those btw) I've ever personally encountered in my amateur, and professional career. Again I was directing this comment at people who think they make no (and by no, i mean so little that the car its dramatically slower, not just a smiedgen down on power) power down low.

So you are sorta half right but when it comes to stuff like this half right can do more harm than good.

Take care Chief.

Wow, there's a lot going on here!

This is off the top of my head. It could be wrong.

There's a few things with cams which can affect idle. To illustrate, here's a cam card and profile map of Tomei's PonCams for the 20v. The map also shows their 16v profile.




Find 0 on the cam map. That's top dead center between the intake and exhaust stroke. So exhaust gases are going out and intake gases are coming in. You'll notice the intake cam opened 12 degrees before this, and the exhaust cam hasn't closed. It will close 19 degrees after this. These 31 degrees are called overlap. At certain engine speeds the momentum of the exhaust gases leaving the chamber is sufficient to decrease the pressure in the chamber further, which increases the pressure differential between the chamber and the intake. This pressure differential is the driving force of the mass flow, so more of it is always better!
At other engine speeds the exhaust valve is open long enough that the pressure differential between the exhaust and chamber can overcome the momentum of the charge and push the exhaust gases back into the chamber. This is called exhaust reversion and is the primary cause of rough idling of large camshafts.
In extreme cases, such as on turbocharged vehicles where exhaust pressure is very high, the pressure differential between the exhaust, chamber, and intake can be bad enough that exhaust gases will be pushed through the chamber and into the intake ports. There's hardly enough time to push up into a plenum and down into any other cylinders. There's a lot of momentum to work against there, and not a lot of time. You'll sometimes see pictures of cylinder heads with soot in the intake bowls. This is caused by extreme exhaust reversion.
It's worth noting that many current car manufacturers are using VVT to cause this reversion and use it as an exhaust gas recirculation system. Sometimes it's a bad thing, like on some 1ZZ-FEs.

Now look at 180 degrees. This is bottom dead center; the end of the intake stroke and the beginning of the compression stroke. You'll notice the intake valve is still open. It will be open for another 72 degrees! A similar thing is going on here; as the piston moves up the pressure in the combustion chamber increases, but the momentum of the intake charge is sufficient to continue pushing more mass into the chamber. Again, at certain engine speeds the intake valve is open long enough that the pressure in the cylinder overcomes the momentum of the charge and pushes some of the contents of the chamber back into the intake manifold. This is called intake reversion. It can raise intake manifold pressure and cause pressure fluctuations, which can make tuning difficult. In this case, a small fraction of this will be exhaust gases, not enough to be concerned about, and once again it will take quite a bit to overcome enough of the intake charge momentum to find its way all the way into a plenum and affect other cylinders.

So there's two things with cam profiles can contribute to idle roughness: exhaust reversion and intake reversion.

As mentioned, though, streetability is a very subjective thing. I'm a big fan of PonCams. They seem to be a great balance, and are VERY capable cams.

SidewaysGts wrote:
A blast from the past! Apologies on the late reply. But No- I did indeed mean exhaust manifold. Thats where exhaustgases come from.

SidewaysGts wrote:

What causes this lopey behavior is the result of how cams of this type behave at low rpms. Cams have whats called "overlap", that is when the intake and exhaust valves are open at the same time. It goes without saying that at lower rpms, the physical window/time frame in which these valve are opened together is physically longer. At low engine speeds this overlap is long enough that a cylinders that is ingesting air, can literally suck exhaust gases straight out of the exhaust manifold from neighboring cylinders which are currently overlapping and have both valves open. This causes improper air/fuel ratios in the cylinder- and they dont fire properly. As the engine speeds pick up this no longer poses an issue.

ITBs which dont share a common chamber, dont suck the exhaust gases back through from neighboring cylinders, and run just fine. This is why an ITB powered car can idle damn near any useable cam profile like it was stock.

Like burdickjp already explained it has nothing to do with sucking exhaust gasses from other cylinders. Even if you had a log style intake or exhaust manifold it's not going to suck in exhaust from other cylinders. Any burst of exhaust gas that is sucked back into the cylinder or even into the intake is going to be from that cylinder only. The behavior on a single cylinder engine will be virtually identical to the behavior on a multi cylinder engine.
Saying that seperating the ITBs will eliminate the problem is total BS. Have you ever triggered the VVT at idle on a 20v? It will barely run.

Ah thank you- But hold up- Isnt that basically exactly what I stated? Sounds to me like youre stating overlap at low rpms can cause exhaust gases (which come from where again, btw?) to be pushed through the intake valves and then into the runners (i jest, this is exactly what you stated- apologies for the redundancy). Now, what exactly did I state? "At low engine speeds this overlap is long enough that a cylinders that is ingesting air, can literally suck exhaust gases straight out of the exhaust manifold from neighboring cylinders which are currently overlapping and have both valves open. This causes improper air/fuel ratios in the cylinder". So... wheres the discrepancy? Again, you've just stated exactly what I had.
Yeah, no that's not exactly what you said. It has nothing to do with the other cylinders.

Sooo.. The "concern has nothing to do with other cylinder sucking in exhaust gasses" it has to do with "Exhaust gasses (that) have been pushed.. into the other chamber (ie: cylinders). Wait. What?...

I never said other chamber. Nothing to do with the other cylinders. You are talking about one dog puking and another coming along and lapping it up. I'm saying it doesn't have anything to do with the other dogs. The dog that is puking is lapping it back up. Doesn't matter if there are other dogs there or not.

A) Ill keep this in mind the next time I see someone running nothing but a high lift/duration camshaft with zero other mods (correction- The first time I see this- As I never have to date) and B) I never said they wouldnt make less power.

Happens pretty often around here. People buy a set of poncams or something similar and throw them in their otherwise stock engine. Some have plans to upgrade other things down the road, others just want the little bump the cams get you. Doing this only looses you a couple hp in the lower RPM but going from 75 hp to 70 hp is worth pointing out. That may be the difference between needing to downshift for a hill or not and on some peoples DD it may be worth expecting. Not a big deal loosing 5 HP but throw in some 288s and go from 75 hp at 4k to 50 hp at 4k might be worth mentioning.

Sorry but the devil is in the details and the big deal you make about it and the way you say it can be misleading to someone. Now they throw some 300 cams in their car and expect it to pull in the mid range like their stock cams did and are pissed because they can't cruise down the highway in fifth any more.
Yeah if they throw some 14:1 pistons in there with a good tune it will probably make about as much power at 3200 RPM but you have to clarify what it will take.

And you spend 99% of your time driving through the rev range where the power should be to get to where the power actually is !
A race cam (300 degree +) needs a lot of engine preparation including a properly ported and flowed head to suit the camshaft, a decent race head will in itself ensure the car is not 'streetable'
As far as 'streetable' cams go I would say anything that can use the stock ecu would be ok.
You need to think cams and gear ratios because that is where the issue will be.

yoshimitsuspeed wrote: Even if you had a log style intake or exhaust manifold it's not going to suck in exhaust from other cylinders

My apologies, but I'm going to have to respectfully disagree

http://www.circletrack.com/enginetech/c ... reversion/

at part-throttle and possibly wide open throttle (WOT), the induction system is operating at a vacuum. Compared to atmospheric pressure, this makes the intake path more suited to combustion residue back-flow than the normal exhaust path. Because the effects of reversion (reverse flow of exhaust gas back into the intake track) include being a function of rpm, it's possible for some other cylinder in the engine to have its next fresh air/fuel charge diluted with exhaust gas from the previously-described cylinder during its exhaust cycle. So, the effects of reversion can, and are, transferred randomly from cylinder to cylinder based on firing order. And the process becomes repeated over and over again throughout the firing order.

After its Quadrajet carburetor was removed, the effects of reversion can be clearly seen on this intake manifold. Note the "cleanest" area of the plenum is in the one of highest exit velocity of the carb; on the primary side and nearest the upper plane's plenum floor. The slower-flowing secondaries and lower plenum floor for the other primary throttle opening all create less flow resistance to reversion. That allows for deeper re-entry into the intake manifold during periods of reversion

Since we are dealing with a "reverse flow" and energy dissipation condition, so-called plenum-runner manifolds (particularly of the single 4V V-type engine design) are more absorptive than individual runner manifolds

In some early reversion studies in which I participated, we were using an inverted, transparent, bowl-shaped cover above an intake manifold's plenum area. With the engine idling and camshaft somewhat advanced, you could actually see little vapor "puffs" blowing back into the plenum area, obviously following the engine's firing order

http://www.crankshaftcoalition.com/wiki ... patibility

Most factory production cams are considered to be short duration cams. This means that the intake valve closes much sooner ABDC than a high performance cam might, and thus less of the intake charge is pushed (reversed, thus the term reversion) past the intake valve back into the intake tract. Since less of the intake charge is lost to reversion, more of it stays in the cylinder, so the compression stroke can yield a satisfactory DCR with a relatively low SCR.

An engine having a lower SCR and an early IVC figure will produce power in the lower RPM range. Since there is little reversion, these engines idle very smoothly (no lope) and will have high idle vacuum around 20 in/Hg

http://www.crankshaftcoalition.com/wiki ... a_camshaft

Overlap and LSA are closely tied together. Increasing overlap contributes to a race cam's choppy idle, along with the intake valve closing point and the exhaust valve opening points. The extra time the valves are open at the same time causes what is called reversion, which is a situation in which the exiting exhaust gasses are partially pushed back up into the intake

http://www.boatheaders.com/reversion.htm

Reversion is simply the exhaust gases momentarily flowing backwards during the overlap phase of the camshaft at low cycling rates. During the overlap phase the engine is on the exhaust stroke and the piston is pushing out the last of the exhaust gases. Prior to reaching top dead center the intake valve begins to open. At low cycling rates the intake charge and the exiting exhaust pulse have yet created any momentum. Thus the piston pushes some spent exhaust gas into the intake manifold. This is why engines with big camshafts idle and sound radical

http://www.austincc.edu/wkibbe/camtheory.htm

The point in the cycle where the intake valve opens is very important. If the intake valve opens too late in the cycle, the initial amount of fuel/air mixture draw into the combustion chamber is reduced and spent gasses will not be effectively flushed from the chamber. If the intake valve opens too early in the cycle, vacuum will be reduced and exhaust gasses will be forced into the intake manifold. When exhaust gasses are forced into the intake manifold, vacuum is adversely affected and the intake runners will soot up. This effect is called "reversion".

http://www.circletrack.com/enginetech/c ... reversion/

When the intake cycle begins, pressure in the intake manifold is less than atmospheric. At the same time, pressure in the cylinder is higher than atmospheric as exhaust residue is being "pumped" out through the exhaust passage. Now the intake valve begins to open. Since intake events begin before the piston reaches BDC on the exhaust stroke (far ahead of this point in racing engines), a "reverse flow" condition (pulse) is directed back into the intake track and against the direction of normal induction flow. While this condition is counter and disruptive to normal such flow, it also includes gaseous and generally non-combustible material we call exhaust gas.

I know I double dipped on a few sites, but this is about 3 minutes worth of googling (its taken me more time to read/quote appropriately than it has to find links talking about this stuff). Mind you I am not asserting that what youve stated (in regards to a cylinder re ingesting its own exhaust) doesnt happen- It does, 100%- Im stating that "this" happens as well.

I would simply like to add that Ive yet to personally cross a single ITB (Or a car using multiple carbs) set up that we couldnt tune to idle pretty damn smoothly at "sane" rpms (1000'ish or so) despite having used some rather aggressive cam profiles and have had rather good success at avoiding that "lopey" idle (Fwiw, We'll quite often have customers request to make the car lopey because of how smoothly we've been able to get their engines to behave at lower rpms/idle) when a relatively "open" intake set up is used (ie velocity stacks or similar). With "Log" manifolds this becomes trickier to accomplish unless the runners are rather long. I've more than once personally seen what kind of difference can be witnessed on a car equipped with itbs by simply removing an intake plenum from the ITBs and nothing else. But hey, I will freely admit that this is "just in my experiences".

[quote=totta crolla] a decent race head will in itself ensure the car is not 'streetable'[/quote]

May inquire why? Thanks.

[quote=totta crolla] a decent race head will in itself ensure the car is not 'streetable'[/quote]

May inquire why? Thanks.

Tell you what you tell me why you think it won't happen first.
I'm sure you can't wait to.....

The first post is the only one that dissagrees with what I'm saying and on an old carbureted V8 with 1.5" long runners I see your claim being much more likely.
The stock 4AGE exhaust manifold is probably about .4 liters per runner so to consume exhaust from another cylinder you would need more than .4 liters of exhaust to flow back up the intake.
The stock NA mani is probably about half that so it would need to consume .2 liters of air to reach the plenum. That is more than half the displacement of the cylinder it's self before the exhaust could even be consumed by another cylinder.
More importantly for the entire runner to be filled with exhaust the cylinder would be consuming 60% exhaust from it's own previous cycle. If this is true then is a little whiff of exhaust from another cylinder really going to have a significant impact on how it idles?
If you separate the intake runners it will still be consuming that 60% exhaust before it can even get any fresh air. How is that going to be any different in the way it runs?

These values are for the smallport NA 16V engine:

Volume runner cilinder 1: 400cc
Volume runner cilinder 2: 375cc
Volume runner cilinder 3: 375cc
Volume runner cilinder 4: 400cc

Volume plenum: 1300cc

Total capacity inlet manifold: 2850cc

BosoHachi wrote:Hey guys, I just wanted to know your opinion on the largest streetable cams
for a DD (but autoxed) ae86.I was leaning towards 288s, are those doable? What
lift would you recommend? I was hoping to get up to a nice 8000-8500rpm red line
(after all of the appropriate valve trainmodifications).
Thanks guys!

According to the HKS cam card, they recommend that the engine be capable of
revving to these levels to take advantage of their cams...

256 degrees duration = 8000 rpm
264 degrees duration = 8300 rpm
272 degrees duration = 8800 rpm
288 degrees duration = ??? but I guess north of 9000 rpm

It is also a recommended that the compression ratio of the engine increase as
the cam duration increases. I don't have a table handy, but I'm sure the info is
out there somewhere So the answer to your question really depends on what
"package" of modifications you are planning on putting together.

But if it helps, I can tell you that I have a standard 10.3:1 compression smallport
with 272 degree cams, ST ITB's and a programmable ECU. This engine idles fine
at 1000 rpm and is even more streetable than a stock bigport. If you have the
factory stock bigport ECU it will work with cams up to 272 degrees. It is starting
to struggle to hold an idle at 272, and gives up with 288 degree cams. NB: I'm
not sure if this applies to both MAP and AFM engines. Maybe someone knows ?

There is a limit to how much lift you can install in a stock 4AGE head... from
memory around 8.3 mm. Lift is more important than duration for a streetable
engine, so get the maximum lift you can. And install HKS or TRD springs to be
on the safe side, as stock springs are close to binding at 8.3 mm lift.

Cheers... jondee86

I'm just gonna watch this one for a while... and see what happens...

oldeskewltoy wrote:I'm just gonna watch this one for a while... and see what happens...

Nothing to see here... move along... move along....

Cheers... jondee86